1) Field of the Invention
The present invention relates to an uncoated polyester filament woven fabric for air bags. More particularly, the present invention relates to an uncoated polyester woven fabric having a tear strength comparable or exceeding that of a nylon filament woven air bag fabric. The fabric has a warp tongue tear resistance of at least 0.75 N/g/m2. Optionally, these fabrics may be further improved with coatings that decrease air permeability through the fabric. Moreover, these fabrics may be produced with a flat type yarn (oval or rectangular in cross-sectional) that also decreases air permeability through the fabric.
2) Prior Art
Polyester industrial filament yarns have a high strength (greater than 70 cN/tex), a high modulus (greater than 170 cN/tex), a low elongation (10-15%), and an excellent dimensional stability. These yarns are predominately used for rubber reinforcements such as in tires and conveyor belts and v-belts. Higher elongation industrial filament yarns can be achieved at the expense of tenacity and modulus by relaxing the drawn yarn. For applications such as air bags, for example, that require high strength and elongation, polyester industrial filament yarns are deficient and polyamide (nylon) yarns are used. Analysis of failed polyester airbags indicates that the primary mode of failure is the tearing of the fabric. This occurs early in the inflation step as the high-pressure gas first enters the folded bag and before the bag is fully inflated. Therefore, there is a need to develop polyester fabric that has a comparable tongue tear strength to that of nylon.
U.S. Pat. No. 5,540,965 to Nishimura et al. discloses a woven polyester air bag obtained by a shrinkage-setting treatment. This patent discloses that the preferred tensile elongation at break is between 9 and 18%. The patent discloses that if the tensile elongation at break is less than 9% the resulting woven fabric may have an unsatisfactory tensile toughness even after the shrinkage-setting procedure. The patent goes on to state that if the tensile elongation at break is more than 18%, the woven fabric may exhibit an insufficient dry shrinkage and become difficult to control relative to the air permeability of the fabric.
U.S. Pat. Nos. 4,977,016, 5,010,633 and 5,073,418 to Thornton et al. disclose a calendered polyester air bag fabric with specific fabric properties but no disclosure on the polyester yarn properties. They do disclose a fabric elongation at break of greater than 25% and a trapezoid tear resistance of greater than 40 pounds (178 N) wherein the fabric is not more than 8.25 ounces per square yard (280 g/m2). These various fabric (and not yarn) properties can be achieved by special weaving techniques etc. It is impossible to tell whether the properties of the fabric are as a direct result of the yarn or the fabric processing, or how they compare to a nylon fabric.
Japanese unexamined publications 2000-27028 and 27029 to Hisao et al. disclose various processes for achieving tough polyester yarn but give no fabric properties. These publications do disclose a relaxation ratio of 12% or higher. The draw ratio and the temperature of various rolls employed in the drawing stage are important to achieving the yarn properties of the invention disclosed.
Japanese unexamined publication 8-269818 to Masataka et al. discloses tough polyester fibers for use in energy absorbing seat belts having a tensile of 8 grams per denier (71 cN/tex) or greater, an elongation at break of 30% or higher. Lastly, this reference discloses a relaxation ratio of 10% or more. This reference gives no woven fabric tear information.
Japanese unexamined publication 7-11512 to Hideharu et al. discloses a polyester fiber with fine silica particles therein. Also incorporated therein is an additive to lower the glass transition temperature all for the purpose of improving the flexural fatigue property. There is no fabric tear strength data, nor a comparison with nylon fabric.
Japanese patent 2289115 to Yoshihiko discloses a polyester fiber having a tenacity of at least 10 grams per denier (88.2 cN/tex) and elongation at break of at least 15%. The highest reported elongation is 18.8%. No fabric properties are disclosed.
Japanese Application 7-186858 to Kozauro et al discloses lightweight polyester air bag fabrics woven from polyester filament yarns having a tenacity of 9 g/denier (79.4 cN/tex) and a breaking elongation of 15%.
European patent 0 442 373 to Swoboda et al discloses a polyester airbag fabric using yarns of low denier. The yarn tenacity was 66 cN/tex with an elongation at break of 19%, and a hot air shrinkage of 4.7% at 200° C. A 26×26 thread/cm 1/1 plain weave fabric had a breaking strength of 255×265 daN with an extension of 34%×26%. (The values indicated on either side of x represent the properties in the warp×weft.) No fabric tear properties were reported.
U.S. Pat. No. 5,236,775 to Swoboda et al discloses an un-calendered, uncoated polyester air bag fabric. No fabric tear data, nor a comparison with a nylon air bag fabric, was given.
U.S. Pat. No. 5,637,114 to Höhnke discloses a polyester uncoated air bag fabric. A 470 dtex, 100 filament yarn was woven in a ripstop construction (5 mm) using 22/22 threads/cm. The yarn had a tenacity of 66.8 cN/tex and a breaking elongation of 21.5% with a hot air shrinkage at 200° C. of 7.4%. The fabric, before washing and drying, had a basis weight of 229 g/m2, a breaking strength/elongation of 297 daN/32% and 325 daN/24% in the warp and weft directions respectively, and a tear strength of 25/24 daN in the warp and weft directions respectively. It is well known that ripstop fabrics will have a higher tear strength than a plain weave.
U.S. Pat. No. 5,902,672 to Swoboda et al discloses a polyester uncoated air bag fabric using a modified huckaback or crepe weave. A ripstop fabric woven from a 315 dtex, 100 filament yarn, with 28 threads/cm, had a basis weight of 197 g/m2 and a tongue tear of 14 daN in both warp and weft directions. No comparison was made to a nylon fabric.
Japanese Application 7-90747 to Nibo et al discloses both nylon and polyester fabrics woven to manufacture, after heat setting and calendaring, an uncoated air bag fabric. The tear strength of the fabrics was measured according to JIS K6328 5.3.6. A direct fabric comparison woven from a 467 dtex, a 216 filament polyester and nylon yarn was made. This showed that a polyester fabric woven at 66×66 ends/inch (26×26 ends/cm) had comparable tensile strength and elongation to a nylon fabric woven at 55×55 ends/inch (21.7×21.7 ends/cm), but an inferior tear strength of 38×36 kg compared to 42×40 kg for the nylon fabric. The basis weight of the fabrics was not disclosed. (The values indicated on either side of x represent the properties in the warp×weft.)
U.S. Pat. Nos. 6,037,047 and 6,147,017 to Fasteneau et al. disclose industrial fibers with non-circular cross-sections that give fabrics with improved cover. The non-circular cross-section of the filament is determined by aspect ratio. These patents disclose aspect ratios in a range from 2-6.
Japanese Application 2002-309462 to Tomomichi et al discloses a nylon airbag fabric woven from flat cross-section yarns that has lower air permeability. No comparison to a polyester airbag was given.
None of the prior art documents teaches how to obtain the balance of properties required for an uncoated fabric with the tongue tear resistance and trapezoidal tear resistance within the range of the present invention that is comparable to or better than nylon. In fact Japanese Application 7-90747 illustrates the inferior fabric tear strength of a polyester fabric compared to a nylon fabric. Further, none of the prior documents discloses that the uncoated fabrics with tear resistance comparable to or better than nylon can be improved (decrease air permeability) with coatings or employing fibers that have a flatter type cross-section (compared to standard round cross-sectional fibers).